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<pre><span class="sourceLineNo">001</span><a name="line.1"></a>
<span class="sourceLineNo">002</span>/*<a name="line.2"></a>
<span class="sourceLineNo">003</span> * Copyright (C) 2011 Archie L. Cobbs. All rights reserved.<a name="line.3"></a>
<span class="sourceLineNo">004</span> *<a name="line.4"></a>
<span class="sourceLineNo">005</span> * $Id: AtomicUpdateFileOutputStream.html 883 2014-05-07 02:45:34Z archie.cobbs $<a name="line.5"></a>
<span class="sourceLineNo">006</span> */<a name="line.6"></a>
<span class="sourceLineNo">007</span><a name="line.7"></a>
<span class="sourceLineNo">008</span>package org.dellroad.stuff.io;<a name="line.8"></a>
<span class="sourceLineNo">009</span><a name="line.9"></a>
<span class="sourceLineNo">010</span>import java.io.File;<a name="line.10"></a>
<span class="sourceLineNo">011</span>import java.io.FileNotFoundException;<a name="line.11"></a>
<span class="sourceLineNo">012</span>import java.io.FileOutputStream;<a name="line.12"></a>
<span class="sourceLineNo">013</span>import java.io.IOException;<a name="line.13"></a>
<span class="sourceLineNo">014</span><a name="line.14"></a>
<span class="sourceLineNo">015</span>/**<a name="line.15"></a>
<span class="sourceLineNo">016</span> * A {@link FileOutputStream} that atomically updates the target file.<a name="line.16"></a>
<span class="sourceLineNo">017</span> *<a name="line.17"></a>
<span class="sourceLineNo">018</span> * &lt;p&gt;<a name="line.18"></a>
<span class="sourceLineNo">019</span> * Instances write to a temporary file until {@link #close} is invoked, at which time the temporary file<a name="line.19"></a>
<span class="sourceLineNo">020</span> * gets {@linkplain File#renameTo renamed} to the target file. This rename operation is atomic on most systems<a name="line.20"></a>
<span class="sourceLineNo">021</span> * (e.g., all UNIX variants). The result is that the target file always exists, and if opened at any time,<a name="line.21"></a>
<span class="sourceLineNo">022</span> * will contain either the previous content or the new content, but never a mix of the two.<a name="line.22"></a>
<span class="sourceLineNo">023</span> * &lt;/p&gt;<a name="line.23"></a>
<span class="sourceLineNo">024</span> *<a name="line.24"></a>
<span class="sourceLineNo">025</span> * &lt;p&gt;<a name="line.25"></a>
<span class="sourceLineNo">026</span> * An open instance can be thought of as representing an open transaction to rewrite the file.<a name="line.26"></a>
<span class="sourceLineNo">027</span> * The "transaction" is committed via {@link #close}, or may be aborted via {@link #cancel} (which<a name="line.27"></a>
<span class="sourceLineNo">028</span> * deletes the temporary file).<a name="line.28"></a>
<span class="sourceLineNo">029</span> * &lt;/p&gt;<a name="line.29"></a>
<span class="sourceLineNo">030</span> */<a name="line.30"></a>
<span class="sourceLineNo">031</span>public class AtomicUpdateFileOutputStream extends FileOutputStream {<a name="line.31"></a>
<span class="sourceLineNo">032</span><a name="line.32"></a>
<span class="sourceLineNo">033</span>    private final File targetFile;<a name="line.33"></a>
<span class="sourceLineNo">034</span><a name="line.34"></a>
<span class="sourceLineNo">035</span>    private File tempFile;<a name="line.35"></a>
<span class="sourceLineNo">036</span>    private long timestamp;<a name="line.36"></a>
<span class="sourceLineNo">037</span><a name="line.37"></a>
<span class="sourceLineNo">038</span>    /**<a name="line.38"></a>
<span class="sourceLineNo">039</span>     * Constructor.<a name="line.39"></a>
<span class="sourceLineNo">040</span>     *<a name="line.40"></a>
<span class="sourceLineNo">041</span>     * @param targetFile the ultimate destination for the output when {@linkplain #close closed}.<a name="line.41"></a>
<span class="sourceLineNo">042</span>     * @param tempFile temporary file that accumulates output until {@linkplain #close close}.<a name="line.42"></a>
<span class="sourceLineNo">043</span>     * @throws FileNotFoundException if {@code tempFile} cannot be opened for any reason<a name="line.43"></a>
<span class="sourceLineNo">044</span>     * @throws SecurityException if a security manager prevents writing to {@code tempFile}<a name="line.44"></a>
<span class="sourceLineNo">045</span>     * @throws NullPointerException if either parameter is null<a name="line.45"></a>
<span class="sourceLineNo">046</span>     */<a name="line.46"></a>
<span class="sourceLineNo">047</span>    public AtomicUpdateFileOutputStream(File targetFile, File tempFile) throws FileNotFoundException {<a name="line.47"></a>
<span class="sourceLineNo">048</span>        super(tempFile);<a name="line.48"></a>
<span class="sourceLineNo">049</span>        this.tempFile = tempFile;<a name="line.49"></a>
<span class="sourceLineNo">050</span>        if (targetFile == null)<a name="line.50"></a>
<span class="sourceLineNo">051</span>            throw new NullPointerException("null targetFile");<a name="line.51"></a>
<span class="sourceLineNo">052</span>        this.targetFile = targetFile;<a name="line.52"></a>
<span class="sourceLineNo">053</span>    }<a name="line.53"></a>
<span class="sourceLineNo">054</span><a name="line.54"></a>
<span class="sourceLineNo">055</span>    /**<a name="line.55"></a>
<span class="sourceLineNo">056</span>     * Convenience constructor.<a name="line.56"></a>
<span class="sourceLineNo">057</span>     *<a name="line.57"></a>
<span class="sourceLineNo">058</span>     * &lt;p&gt;<a name="line.58"></a>
<span class="sourceLineNo">059</span>     * This constructor uses a temporary file within the same directory as {@code targetFile}.<a name="line.59"></a>
<span class="sourceLineNo">060</span>     *<a name="line.60"></a>
<span class="sourceLineNo">061</span>     * @param targetFile the ultimate destination for the output when {@linkplain #close closed}.<a name="line.61"></a>
<span class="sourceLineNo">062</span>     * @throws FileNotFoundException if {@code tempFile} cannot be opened for any reason<a name="line.62"></a>
<span class="sourceLineNo">063</span>     * @throws IOException if a temporary file could not be created<a name="line.63"></a>
<span class="sourceLineNo">064</span>     * @throws SecurityException if a security manager prevents writing to {@code tempFile}<a name="line.64"></a>
<span class="sourceLineNo">065</span>     * @throws NullPointerException if either parameter is null<a name="line.65"></a>
<span class="sourceLineNo">066</span>     */<a name="line.66"></a>
<span class="sourceLineNo">067</span>    public AtomicUpdateFileOutputStream(File targetFile) throws IOException {<a name="line.67"></a>
<span class="sourceLineNo">068</span>        this(targetFile, File.createTempFile("atomicupdate", null, targetFile.getParentFile()));<a name="line.68"></a>
<span class="sourceLineNo">069</span>    }<a name="line.69"></a>
<span class="sourceLineNo">070</span><a name="line.70"></a>
<span class="sourceLineNo">071</span>    /**<a name="line.71"></a>
<span class="sourceLineNo">072</span>     * Get the target file.<a name="line.72"></a>
<span class="sourceLineNo">073</span>     *<a name="line.73"></a>
<span class="sourceLineNo">074</span>     * @return target file, never null<a name="line.74"></a>
<span class="sourceLineNo">075</span>     */<a name="line.75"></a>
<span class="sourceLineNo">076</span>    public synchronized File getTargetFile() {<a name="line.76"></a>
<span class="sourceLineNo">077</span>        return this.targetFile;<a name="line.77"></a>
<span class="sourceLineNo">078</span>    }<a name="line.78"></a>
<span class="sourceLineNo">079</span><a name="line.79"></a>
<span class="sourceLineNo">080</span>    /**<a name="line.80"></a>
<span class="sourceLineNo">081</span>     * Get the temporary file.<a name="line.81"></a>
<span class="sourceLineNo">082</span>     *<a name="line.82"></a>
<span class="sourceLineNo">083</span>     * &lt;p&gt;<a name="line.83"></a>
<span class="sourceLineNo">084</span>     * If this instance has already been {@linkplain #close closed} (either successfully or not)<a name="line.84"></a>
<span class="sourceLineNo">085</span>     * or {@linkplain #cancel canceled}, this will return null.<a name="line.85"></a>
<span class="sourceLineNo">086</span>     *<a name="line.86"></a>
<span class="sourceLineNo">087</span>     * @return temporary file, or null if {@link #close} or {@link #cancel} has already been invoked<a name="line.87"></a>
<span class="sourceLineNo">088</span>     */<a name="line.88"></a>
<span class="sourceLineNo">089</span>    public synchronized File getTempFile() {<a name="line.89"></a>
<span class="sourceLineNo">090</span>        return this.tempFile;<a name="line.90"></a>
<span class="sourceLineNo">091</span>    }<a name="line.91"></a>
<span class="sourceLineNo">092</span><a name="line.92"></a>
<span class="sourceLineNo">093</span>    /**<a name="line.93"></a>
<span class="sourceLineNo">094</span>     * Cancel this instance. This "aborts" the open "transaction", and deletes the temporary file.<a name="line.94"></a>
<span class="sourceLineNo">095</span>     *<a name="line.95"></a>
<span class="sourceLineNo">096</span>     * &lt;p&gt;<a name="line.96"></a>
<span class="sourceLineNo">097</span>     * Does nothing if {@link #close} or {@link #cancel} has already been invoked.<a name="line.97"></a>
<span class="sourceLineNo">098</span>     */<a name="line.98"></a>
<span class="sourceLineNo">099</span>    public synchronized void cancel() {<a name="line.99"></a>
<span class="sourceLineNo">100</span>        if (this.tempFile != null) {<a name="line.100"></a>
<span class="sourceLineNo">101</span><a name="line.101"></a>
<span class="sourceLineNo">102</span>            // Close output stream to release file descriptor<a name="line.102"></a>
<span class="sourceLineNo">103</span>            try {<a name="line.103"></a>
<span class="sourceLineNo">104</span>                super.close();<a name="line.104"></a>
<span class="sourceLineNo">105</span>            } catch (IOException e) {<a name="line.105"></a>
<span class="sourceLineNo">106</span>                // ignore<a name="line.106"></a>
<span class="sourceLineNo">107</span>            }<a name="line.107"></a>
<span class="sourceLineNo">108</span><a name="line.108"></a>
<span class="sourceLineNo">109</span>            // Delete temporary file<a name="line.109"></a>
<span class="sourceLineNo">110</span>            this.tempFile.delete();<a name="line.110"></a>
<span class="sourceLineNo">111</span>            this.tempFile = null;<a name="line.111"></a>
<span class="sourceLineNo">112</span>        }<a name="line.112"></a>
<span class="sourceLineNo">113</span>    }<a name="line.113"></a>
<span class="sourceLineNo">114</span><a name="line.114"></a>
<span class="sourceLineNo">115</span>    /**<a name="line.115"></a>
<span class="sourceLineNo">116</span>     * Close this instance. This "commits" the open "transaction".<a name="line.116"></a>
<span class="sourceLineNo">117</span>     *<a name="line.117"></a>
<span class="sourceLineNo">118</span>     * &lt;p&gt;<a name="line.118"></a>
<span class="sourceLineNo">119</span>     * If successful, the configured {@code tempFile} will be {@linkplain File#renameTo renamed}<a name="line.119"></a>
<span class="sourceLineNo">120</span>     * to the configured destination file {@code targetFile}. In any case, after this method returns<a name="line.120"></a>
<span class="sourceLineNo">121</span>     * (either normally or abnormally), the temporary file will be deleted.<a name="line.121"></a>
<span class="sourceLineNo">122</span>     *<a name="line.122"></a>
<span class="sourceLineNo">123</span>     * @throws IOException if {@link #close} or {@link #cancel} has already been invoked<a name="line.123"></a>
<span class="sourceLineNo">124</span>     */<a name="line.124"></a>
<span class="sourceLineNo">125</span>    @Override<a name="line.125"></a>
<span class="sourceLineNo">126</span>    public synchronized void close() throws IOException {<a name="line.126"></a>
<span class="sourceLineNo">127</span><a name="line.127"></a>
<span class="sourceLineNo">128</span>        // Sanity check<a name="line.128"></a>
<span class="sourceLineNo">129</span>        if (this.tempFile == null)<a name="line.129"></a>
<span class="sourceLineNo">130</span>            throw new IOException("already closed or canceled");<a name="line.130"></a>
<span class="sourceLineNo">131</span><a name="line.131"></a>
<span class="sourceLineNo">132</span>        // Close temporary file<a name="line.132"></a>
<span class="sourceLineNo">133</span>        super.close();<a name="line.133"></a>
<span class="sourceLineNo">134</span><a name="line.134"></a>
<span class="sourceLineNo">135</span>        // Read updated modification time<a name="line.135"></a>
<span class="sourceLineNo">136</span>        final long newTimestamp = this.tempFile.lastModified();<a name="line.136"></a>
<span class="sourceLineNo">137</span><a name="line.137"></a>
<span class="sourceLineNo">138</span>        // Rename file, or delete it if that fails<a name="line.138"></a>
<span class="sourceLineNo">139</span>        try {<a name="line.139"></a>
<span class="sourceLineNo">140</span>            if (!this.tempFile.renameTo(this.targetFile)) {<a name="line.140"></a>
<span class="sourceLineNo">141</span>                throw new IOException("error renaming temporary file `" + this.tempFile.getName()<a name="line.141"></a>
<span class="sourceLineNo">142</span>                  + "' to `" + this.targetFile.getName() + "'");<a name="line.142"></a>
<span class="sourceLineNo">143</span>            }<a name="line.143"></a>
<span class="sourceLineNo">144</span>            this.tempFile = null;<a name="line.144"></a>
<span class="sourceLineNo">145</span>        } finally {<a name="line.145"></a>
<span class="sourceLineNo">146</span>            if (this.tempFile != null)          // exception thrown, cancel transaction<a name="line.146"></a>
<span class="sourceLineNo">147</span>                this.cancel();<a name="line.147"></a>
<span class="sourceLineNo">148</span>        }<a name="line.148"></a>
<span class="sourceLineNo">149</span><a name="line.149"></a>
<span class="sourceLineNo">150</span>        // Update target file timestamp<a name="line.150"></a>
<span class="sourceLineNo">151</span>        this.timestamp = newTimestamp;<a name="line.151"></a>
<span class="sourceLineNo">152</span>    }<a name="line.152"></a>
<span class="sourceLineNo">153</span><a name="line.153"></a>
<span class="sourceLineNo">154</span>    /**<a name="line.154"></a>
<span class="sourceLineNo">155</span>     * Get the last modification timestamp of the target file as it was at the time it was updated by this instance.<a name="line.155"></a>
<span class="sourceLineNo">156</span>     *<a name="line.156"></a>
<span class="sourceLineNo">157</span>     * &lt;p&gt;<a name="line.157"></a>
<span class="sourceLineNo">158</span>     * This method only works after {@link #close} has been successfully invoked, otherwise it returns zero.<a name="line.158"></a>
<span class="sourceLineNo">159</span>     *<a name="line.159"></a>
<span class="sourceLineNo">160</span>     * @return target file modification time, or zero if {@link #close} has not been successfully invoked<a name="line.160"></a>
<span class="sourceLineNo">161</span>     */<a name="line.161"></a>
<span class="sourceLineNo">162</span>    public synchronized long getTimestamp() {<a name="line.162"></a>
<span class="sourceLineNo">163</span>        return this.timestamp;<a name="line.163"></a>
<span class="sourceLineNo">164</span>    }<a name="line.164"></a>
<span class="sourceLineNo">165</span><a name="line.165"></a>
<span class="sourceLineNo">166</span>    /**<a name="line.166"></a>
<span class="sourceLineNo">167</span>     * Ensure the temporary file is deleted in cases where this instance never got successfully closed.<a name="line.167"></a>
<span class="sourceLineNo">168</span>     */<a name="line.168"></a>
<span class="sourceLineNo">169</span>    @Override<a name="line.169"></a>
<span class="sourceLineNo">170</span>    protected void finalize() throws IOException {<a name="line.170"></a>
<span class="sourceLineNo">171</span>        try {<a name="line.171"></a>
<span class="sourceLineNo">172</span>            if (this.tempFile != null)<a name="line.172"></a>
<span class="sourceLineNo">173</span>                this.cancel();<a name="line.173"></a>
<span class="sourceLineNo">174</span>        } finally {<a name="line.174"></a>
<span class="sourceLineNo">175</span>            super.finalize();<a name="line.175"></a>
<span class="sourceLineNo">176</span>        }<a name="line.176"></a>
<span class="sourceLineNo">177</span>    }<a name="line.177"></a>
<span class="sourceLineNo">178</span>}<a name="line.178"></a>




























































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